Application of the Langmuir and Freundlich equations for the removal of Cd2++ and Pb2+ ions by adsorption on to natural clay minerals

Abstract

Metal ion sorption plays a critical role in mitigating environmental pollution. However, there is a dearth of research data on the sorption characteristics of Cd²⁺ and Pb2⁺ ions on natural clay minerals in Akwa Ibom State, Nigeria. This study aims to investigate the sorption behaviour of Cd²⁺ and Pb²⁺ ions on natural clay minerals using the Langmuir and Freundlich equations. Four samples of natural clay were collected from Ikot Ebom Itam, in Itu and were used for this study. Samples were characterized using standard analytical methods including X-ray fluorescence (XRF), X-ray diffraction (XRD) and Atomic Absorption Spectrophotometry (AAS). Results showed the elemental components to be more of silica and alumina as the predominant constituents, whereas EXRD analysis showed that the patterns of all four samples comprised predominantly crystalline phases of kaolinite (Al₂Si₂O₅(OH)₄), and quartz (Si₆O₆) except for sample CSA whose peaks were attributable to goethite (α-FeO(OH)). Results of metal analysis showed Cd, Pb and Fe concentrations (in ppm) ranged from 0.003-0.007, 1.04-1.76 and 0.54-13.54, respectively. The percentage composition of C, H, N and S ranged from 41 to 50%, 3 to 5%, 0 to 1% and 0 to 1% respectively. The EDXRF analysis shows that the clay minerals exhibited greater sorption capacities for Cd²⁺ and Pb²⁺ ions from aqueous solutions due to high levels of Fe and Al oxides. The Langmuir and Freundlich models were applied to study the sorption characteristics using Pearson correlation analysis. The Freundlich isotherm model offered the optimum option for Cd (R² = 0.9548) sorption and Langmuir model for Pb (0.9940). Results shows that the sorption of these toxic metals on clay minerals which is dependent on pH, initial concentration of adsorbate and type of adsorbent can reduce their concentrations and mobility in aqueous solution and natural environment. Based on the study, it can be said that clay can be used as a less expensive and effective adsorbent in removal of Cd²⁺ and Pb²⁺ ions from aqueous solutions.